Optical thresholding apparatus and method

Abstract

An apparatus and method for processing optical beams designed to adaptively spatially threshold or filter an intensity histogram spectrum for re-transformation to a two-dimensional thresholded optical output. Such apparatus and method is used in optical computing and logic processing to selectively pass only certain light intensities, thereby blocking undesirable background noise while passing the desired signals. An incoming histogram light beam, containing an optical position distribution corresponding to the intensity distribution of an original optical beam, is split into first and second beams. The first beam is directed at a light detector array which transforms the optical position intensities of the first bema into directly proportional electrical signals. These signals are sent to a microprocessor which analyzes this input, determines the intensity distribution, calculates the algebraic mean and variance, sets the intensity threshold level based on pre-set information, and sends an electronic voltage signal to an optical selective reflector. The optical reflector, preferably a CCD LCLV, is positioned to receive the second split beam, and is instructed by the electronic voltage signal to selectively reflect only certain optical intensities onto an inverse Fourier transform lens. This lens re-transforms the quasi-one-dimensional second split beam into the desired two-dimensional thresholded optical output.

We claim: 
     
       1. An optical thresholding apparatus for establishing a threshold optical intensity level for an input optical beam and removing portions of the beam below said level, the optical beam being characterized by a spatial intensity distribution, comprising: means for transforming the input beam into a histogram beam having a positional distribution which corresponds to the intensity histogram distribution of the input beam,   sensing means positioned to sense at least a portion of the histogram beam, said sensing means responding to the histogram beam to establish a desired threshold intensity level for the input beam and a corresponding threshold positional level for the histogram beam, and transforming said threshold levels into a threshold-specified output signal,   a light valve positioned to receive at least a portion of the histogram beam and connected to receive said threshold-specified output signal, said light valve being responsive to said signal to output a thresholded histogram beam having a thresholded positional distribution which corresponds to said desired threshold intensity level for the input beam, and   means for transforming said thresholded histogram beam into an output beam having substantially the spatial intensity distribution of the input beam subject to said desired threshold intensity level.   
     
     
       2. The optical threshold apparatus of claim 1, said means for transforming the input beam into a histogram beam comprising an intensity-to-angle mapping generator and a Fourier transform lens, and said means for transforming said thresholded histogram beam into an output beam comprising an inverse Fourier transform lens. 
     
     
       3. An optical thresholding apparatus for thresholding a histogram light beam which contains an optical position distribution corresponding to the spatial intensity distribution of an original optical beam, comprising: means positioned to sense at least a portion of the histogram light beam, to determine therefrom the intensity distribution of the original beam, to calculate a desired intensity threshold level from said intensity distribution, to transform said desired intensity threshold to a corresponding positional threshold in the histogram beam, and to generate a threshold-specified output signal representing said positional threshold; and   a light valve positioned to receive at least a portion of said histogram beam and connected to receive said threshold-specified output signal, said light valve being responsive to said signal to output a beam having substantially the positional distribution of the histogram beam subject to said threshold positional level.   
     
     
       4. The optical thresholding apparatus of claim 3, wherein the light valve is governed by the threshold-specified output signal from the sensing means to output only those histogram beam positions which correspond to the original optical beam intensities exceeding said threshold intensity. 
     
     
       5. The optical thresholding apparatus of claim 3, wherein said sensing means comprises the combination of a detector which detects the histogram beam and generates signals representing the positional distribution of said beam, and a signal processing means connected to receive said generated signals and to establish therefrom said positional threshold. 
     
     
       6. The optical thresholding apparatus of claim 5, wherein said signal processing means comprises a computer. 
     
     
       7. The optical threshold apparatus of claim 6, wherein said light valve comprises a charge-coupled device liquid crystal light valve. 
     
     
       8. An optical thresholding apparatus for thresholding a histogram light beam which contains an optical positional distribution corresponding to the intensity distribution of an original optical beam, comprising: means for splitting the histogram beam into first and second beams which retain the positional distribution of the histogram beam;   means positioned to detect said first beam and to generate signals representing the positional distribution of said first beam;   signal processing means connected to receive said signals from said detection means, to determine therefrom a desired intensity threshold level for the original beam, and to generate a threshold-specified output corresponding to said intensity threshold for the original beam; and   electro-optical processing means positioned to receive said second beam and connected to receive said threshold-specified output signal, said processing means being responsive to said signal to produce an output beam which comprises the portions of said second beam on one side of said positional threshold.   
     
     
       9. The optical thresholding apparatus of claim 8, wherein said electro-optical processing means is responsive to said signal to produce an output beam which comprises the portions of said second beam which exceed said threshold positional level. 
     
     
       10. The optical thresholding apparatus of claim 9, wherein the signal processing means determines the desired intensity threshold level from the signals received from said detection means by generating the original optical beam intensity distribution therefrom, calculating the algebraic mean and variance of said intensity distribution, setting the desired threshold intensity level at a predetermined multiple of variances, transforming said desired intensity threshold to a corresponding positional threshold in the histogram beam, and generating a threshold-specified output signal representing said positional threshold. 
     
     
       11. The optical thresholding apparatus of claim 10, wherein said signal processing means comprises a computer. 
     
     
       12. The optical thresholding apparatus of claim 8, wherein said electro-optical processing means comprises a charge-coupled device liquid crystal light valve. 
     
     
       13. An optical thresholding apparatus for thresholding a histogram light beam which contains an optical positional distribution corresponding to the intensity distribution of an original optical beam, comprising: a beam splitter positioned to split the histogram beam into first and second split beams;   an optical beam detector positioned so as to detect said first beam and to generate signals representative thereof;   a signal processor connected to receive the signals from said detection means, to determine therefrom the original optical beam intensity distribution, to calculate mathematical parameters of said intensity distribution and a desired threshold intensity level from said mathematical desired parameters, to transform said desired intensity threshold to a corresponding positional threshold in the histogram beam, and to generate a threshold-specified output signal representing said positional threshold; and   an optical reflector positioned to reflect said second beam and connected to receive said threshold-specified output signal to adjust said reflection in accordance with said positional threshold.   
     
     
       14. The optical thresholding apparatus of claim 13, wherein said optical reflector comprises a charge-coupled device liquid crystal light valve. 
     
     
       15. The optical thresholding apparatus of claim 14, wherein said optical reflector is constrained by said threshold-specified output signal to reflect only those histogram beam positions corresponding to the original optical beam intensities which exceed said threshold positional level, and to block all other histogram beam positions. 
     
     
       16. The optical thresholding apparatus of claim 15, wherein said signal processor comprises a computer. 
     
     
       17. A method for thresholding optical beam intensities so as to block some intensities and pass others within a histogram light beam which contains an optical position distribution corresponding to the intensity distribution of an original optical beam, comprising: splitting said histogram beam into first and second beams;   directing said first beam to an optical beam detector and said second beam to an optical reflector;   detecting said first beam and generating therefrom a series of electrical signals with electrical intensities directly proportional to the optical position intensities of said first beam to be fed to a signal processor;   processing said series of electrical signals to determine therefrom the original optical beam intensity distribution, calculating a desired intensity threshold level from said intensity distribution, transforming said desired intensity threshold to a corresponding positional threshold in the histogram beam, and generating a threshold-specified output signal representing said positional threshold; and   optically reflecting said second beam, and adjusting said optical reflection in response to the electrical signal received from the signal processor to reflect only those histogram beam positions corresponding to the original optical beam intensity distribution which are greater than the threshold positional level, and to block all other histogram positions.   
     
     
       18. The method of claim 17, wherein light reflected from the optical reflector passes through the beam splitter essentially unchanged and continues onto a focusing lens. 
     
     
       19. The method of claim 17, wherein the intensity threshold level is determined during the signal processing step by multiplying a pre-set real number variable with the calculated variance and adding the product to a preset starting position variable. 
     
     
       20. The method of claim 19, wherein said starting position variable is a designated level of the intensity distribution. 
     
     
       21. The method of claim 20, wherein the threshold intensity level and pre-set real number are both time-varying.